1. Field of the Invention
The present invention relates to a monolithic electronic device. More particularly, the present invention relates to a monolithic electronic device included in an RF electric circuit.
2. Description of the Related Art
A monolithic LC filter 1 shown in FIG. 7 is a typical monolithic electronic device. The monolithic LC filter 1 includes two LC bandpass filters. The monolithic LC filter 1 includes a first insulation sheet 2, a shield electrode 11 on a second insulation sheet 2, capacitor electrodes 8b and 9b on a third insulation sheet 2, inductor electrodes 4b and 5b on a fourth insulation sheet 2, a coupling capacitor electrode 12 on a fifth insulation sheet 2, inductor electrodes 4a and 5a on a sixth insulation sheet 2, capacitor electrodes 8a and 9a on a seventh insulation sheet 2, and a shield electrode 10 on an eighth insulation sheet 2.
One end of each of the inductor electrodes 4b and 5b is exposed at the front of the fourth insulation sheet 2. The widths of the other ends, which are indicated by reference numerals 6b and 7b, are larger than those of the inductor electrodes 4b and 5b. The other ends 6b and 7b function as capacitor electrodes. An input lead electrode 14b extends from the middle of the inductor electrode 4b and is exposed at the left side of the fourth insulation sheet 2. Further, an input lead electrode 15b extends from the middle of the inductor electrode 5b and is exposed at the right side of the fourth insulation sheet 2.
One end of each of the inductor electrodes 4a and 5a is exposed at the front of the sixth insulation sheet 2. The widths of the other ends, which are indicated by reference numerals 6a and 7a, are larger than those of the inductor electrodes 4a and 5a. The other ends 6a and 7a function as capacitor electrodes. An input lead electrode 14a extends from the middle of the inductor electrode 4a and is exposed at the left side of the sixth insulation sheet 2. Further, an input lead electrode 15a extends from the middle of the inductor electrode 5a and is exposed at the right side of the sixth insulation sheet 2.
One end of each of the capacitor electrodes 8a and 8b is exposed at the back of the seventh insulation sheet 2 and the third insulation sheet 2. The capacitor electrode 8a is opposed to the other end 6a of the inductor electrode 4a and the capacitor electrode 8b is opposed to the other end 6b of the inductor electrode 4b, whereby a capacitor C1 is provided. Further, the inductor electrodes 4a and 4b define a dual inductor L1. The capacitor C1 and the dual inductor L1 define an LC parallel resonant circuit. Thus, a first LC resonator Q1 is provided.
One end of each of the capacitor electrodes 9a and 9b is exposed at the back of the seventh insulation sheet 2 and the third insulation sheet 2. The capacitor electrode 9a is opposed to the other end 7a of the inductor electrode 5a and the capacitor electrode 9b is opposed to the other end 7b of the inductor electrode 5b, whereby a capacitor C2 is provided. Further, the inductor electrodes 5a and 5b define a dual inductor L2. The capacitor C2 and the dual inductor L2 define an LC parallel resonant circuit. Thus, a second LC resonator Q2 is provided.
The coupling capacitor electrode 12 is opposed to the other ends 6a, 6b, 7a, and 7b to define a coupling capacitor Cs1 (not shown).
The shield electrode 10, which has a large area, has extensions 10a, 10b, 10c, 10d, 10e, 10f, 10g, 10h, 10i, and 10j. The extensions 10a to 10j are exposed at the four sides of the eighth shield electrode 2.
The shield electrode 11, which has a large area, has extensions 11a, 11b, 11c, 11d, 11e, 11f, 11g, 11h, 11i, and 11j. The extensions 11a to 11j are exposed at the four sides of the second shield electrode 2.
The first to eighth insulation sheets 2 are laminated in the order shown in FIG. 7. Then, the laminated insulation sheets 2 are integrally fired and formed into a composite 15 shown in FIG. 8. Further, as shown in FIG. 9, a conductive paste is applied to the front and the back of the composite 15 by a dipping method. Then, the conductive paste is fired, whereby side surface ground external electrodes 18 and 19 are formed. At that time, bent portions 18a and 19a of the side surface ground external electrodes 18 and 19 are formed on the top surface, the bottom surface, the left surface, and the right surface of the composite 15. One end of each of the inductor electrodes 4a to 5b, the extensions 10a to 10c of the shield electrode 10, and the extensions 11a to 11c of the shield electrode 11 are connected to the side surface ground external electrode 18. One end of each of the capacitor electrodes 8a to 9b, the extensions 10f to 10h of the shield electrode 10, and the extensions 11f to 11h of the shield electrode 11 are connected to the side surface ground external electrode 19.
Then, as shown in FIG. 10, a conductive paste is applied to both sides of the composite 15 by a transfer printing method and fired. Subsequently, an input external electrode 16, an output external electrode 17, and end surface ground external electrodes 20, 21, 22, and 23 are formed. At that time, bent portions 16a, 17a, 20a, 21a, 22a, and 23a are formed on the top surface and the bottom surface of the composite 15. The end surface ground external electrodes 20 and 21 are electrically connected to the side surface ground external electrode 18. The end surface ground external electrodes 22 and 23 are electrically connected to the side surface ground external electrode 19. The input lead electrodes 14a and 14b are connected to the input external electrode 16. The output lead electrodes 15a and 15b are connected to the output external electrode 17.
The bent portions 16a to 23a have an influence on the characteristics of the LC filter 1 because, for example, they overlap the inductor electrodes 4a, 4b, 5a, and 5b, and so forth. Subsequently, a variation in the dimensions of the bent portions 16a to 23a causes the electrical characteristics of the LC filter 1 to vary. However, in the case of the known LC filter 1, the bent portions 16a to 23a and the external electrodes 16 to 23 are formed at the same time. In such a case, it becomes difficult to reliably form the bent portions 16a to 23a. Therefore, the variation in the dimensions of the bent portions 16a to 23a becomes large. Accordingly, the electrical characteristics of the LC filter 1 tend to vary greatly.
The adhesion strength of the insulation sheets and the electrodes of the monolithic electronic device is low. Therefore, when the shield electrodes 10 and 11, which each have a large area, are laminated, an opening is formed between each of the extensions 10a to 10j and 11a to 11j. The openings are formed in order to prevent delamination of the composite 15. That is to say, the areas of the shield electrodes 10 and 11, which are in contact with the insulation sheets 2, are reduced, since delamination tends to occur with relative ease at the edge portions of the insulation sheets 2. However, the areas of the insulation sheets which are in contact with each other are increased. In particular, large openings are formed between the extensions 10j and 10a of the shield electrode 10 and between the extensions 11j and 11a of the shield electrode 11, and so forth because delamination tends to occur there due to internal stresses that tend to be exerted on the corners of the composite 15.
When such openings are formed, however, electric fields and magnetic fields leak through the openings. Subsequently, the electrical characteristics of the monolithic electronic device are deteriorated (emission loss). Therefore, as shown in FIG. 11, the openings of the LC filter 1 are blocked by the bent portions 20a to 23a of the external electrodes 20 to 23. However, the variation in the shape of the bent portions 20a to 23a is large, and the size of the bent portions is limited. Therefore, it has been difficult to reliably and fully cover such openings with the bent portions 20a to 23a. 
Further, in order to make the bent portions 16a, 17a, 20a, 21a, 22a, and 23a having predetermined sizes which are large enough for mounting the LC filter 1 on a printed board, the processing condition of the external electrodes 16, 17, and 20 to 23 becomes increasingly severe, and the productivity is significantly decreased.
In order to overcome the problems described above, preferred embodiments of the present invention provide a monolithic electronic device that has minimal variation in the dimensions of bent portions of the external electrodes thereof and that achieves very stable electrical characteristics.
A monolithic electronic device according to a preferred embodiment of the present invention includes a composite including insulation layers laminated together, at least one internal circuit element, and at least one shield electrode having a plurality of extensions. Further, the monolithic electronic device includes an input external electrode and an output external electrode that are disposed on the composite and ground external electrodes that are disposed on the composite and are electrically connected to the plurality of extensions. Each of the input external electrode and the output external electrode has a main electrode portion that is defined by a conductive paste disposed on an end surface of the composite. The ground external electrodes include a side surface segment that is defined by conductive paste disposed on the entirety of a side surface of the composite. Each of the ground external electrodes has a bent segment that is formed by any one of pattern printing, thin-film forming, and photolithography on at least one of the top surface and the bottom surface of the composite. The bent segments cover openings between the plurality of extensions of the shield electrode in plan view. As the internal circuit element, a capacitor or an inductor may be used.
Preferably, the bent segments of the ground external electrodes have a substantially U-shaped configuration so as to cover at least openings between the extensions at the corners of the shield electrode. The ground external electrodes may further include an end surface segment that is formed by applying a conductive paste onto an end surface of the composite. The width of the center portions of the bent segments of the ground external electrodes may be smaller than the width at both ends of the bent segments of the ground external electrodes. The plurality of extensions of the shield electrode may include an extension connected to the side surface segment and an extension connected to the end surface segment.
According to the above-described configuration, bent portions of the side surface segments and the end surface segments, which are formed by applying the conductive paste, are formed in the areas of the bent segments, which are formed by pattern printing, photolithography, or a thin-film forming method. Therefore, the dimensions of the bent portions are determined by the dimensions of the bent segments. Subsequently, the variation in the dimensions of the bent portions is reduced. Further, the bent segments cover openings between the extensions of the shield electrode. Therefore, the leakage of electric fields and magnetic fields from the openings is prevented, and the emission loss is reduced. Accordingly, the monolithic electronic device has minimal variation in the dimensions of bent portions of the external electrodes and reliably achieves very stable electrical characteristics.
Further, since the input external electrode and the output external electrode each have a bent segment that is formed by any one of pattern printing, thin-film forming, and photolithography on at least one of the top surface and the bottom surface of the composite, the dimensions of the bent portions of the input external electrode and the output external electrode become constant and the expansion of solder on the bent portions is stabilized. Therefore, when the monolithic electronic device is mounted on a printed circuit board or other suitable substrate, shorting, due to solder bridging, across the input external electrode, the output external electrode, and the ground external electrodes is prevented and minimized.
Other features, elements, steps, characteristics and advantages of the present invention will be described with respect to preferred embodiments thereof with reference to the attached drawings.